Clean up the Dockerfile and secure the build process
Clean up the Dockerfile and secure the build process

- Create a home directory for the new unprivileged user so that programs
  have a place to put things.
- Can run `lein` inside the container without running into
  permissions issues.
- Build system now drops privileges earlier and runs the build process
  as the unprivileged user.
- Use of COPY --chown=... makes it possible to perform file ownership
  operations as root while continuing to run arbitrary commands as the
  unprivileged user.

democracyworks/electorate-works